zenith is the angle between the center of the sun
and a line perpendicular to earth's surface. It defaults to
date.sunrise_zenith

Common zenith angles

Angle

Description

90°50'

Sunrise: the point where the sun becomes visible.

96°

Civil twilight: conventionally used to signify the start of dawn.

102°

Nautical twilight: the point at which the horizon starts being visible at sea.

108°

Astronomical twilight: the point at which the sun starts being the source of any illumination.

gmtoffset

Specified in hours.
The gmtoffset is ignored, if
format is
SUNFUNCS_RET_TIMESTAMP.

Return Values

Returns the sunrise time in a specified format on
success or FALSE on failure. One potential reason for failure is that the
sun does not rise at all, which happens inside the polar circles for part of
the year.

Errors/Exceptions

Every call to a date/time function will generate a E_NOTICE
if the time zone is not valid, and/or a E_STRICT
or E_WARNING message
if using the system settings or the TZ environment
variable. See also date_default_timezone_set()

After some searching, I finally found a website that can calculate the sun's zenith. Just look up your city's lat/long (remember, west/south are negative even if it doesn't show where you look up the lat/long) and the time of sunrise/sunset and use this site: